- Takuji Ohyama
- Tokyo University of Agriculture
- Niigata University
We are investigating on the effects of nitrate on nodule growth and nitrogen fixation activity in soybean root nodules. Soybean is a globally important legume crop that provides proteins and lipids to humans and livestock. Soybean plants can form root nodules and utilize atmospheric N2 in association with rhizobia, which are nitrogen-fixing soil bacteria. However, it is well known that nodulation and the nitrogen fixation activity of root nodules are suppressed when the nodulated roots are exposed to a high concentration of combined nitrogen. Nitrate, a major form of inorganic nitrogen in the upland soil, inhibits nodulation, nodule growth, and N2 fixation activity in soybean plants. We are studing on the mechanisms of nitrate inhibition from physiological, molecular studies.
We developed a new fertilization technique a deep placement of coated urea or lime nitrogen at the depth of 20 cm. This fertilization promoted soybean growth and seed yield without repressing nitrogen fixation.